A number of systems and programs are offered on the market for the design, the engineering and the manufacturing of objects. CAD is an acronym for Computer-Aided Design, e.g. it relates to software solutions for designing an object. CAE is an acronym for Computer-Aided Engineering, e.g. it relates to software solutions for simulating the physical behavior of a future product. CAM is an acronym for Computer-Aided Manufacturing, e.g. it relates to software solutions for defining manufacturing processes and operations. In such systems, the graphical user interface (GUI) plays an important role as regards the efficiency of the technique. These techniques may be embedded within Product Lifecycle Management (PLM) systems. PLM refers to a business strategy that helps companies to share product data, apply common processes, and leverage corporate knowledge for the development of products from conception to the end of their life, across the concept of extended enterprise.
The PLM solutions provided by Dassault Systemes (under the trademarks CATIA, ENOVIA and DELMIA) provide an Engineering Hub, which organizes product engineering knowledge, a Manufacturing Hub, which manages manufacturing engineering knowledge, and an Enterprise Hub which enables enterprise integrations and connections into both the Engineering and Manufacturing Hubs. All together the system delivers an open object model linking products, processes, resources to enable dynamic, knowledge-based product creation and decision support that drives optimized product definition, manufacturing preparation, production and service.
Many CAD systems now allow the user to design a 3D modeled object, based on a boundary representation (B-Rep) of the modeled object provided to the user. The B-Rep is a data format comprising a set of faces each defined as a bounded portion of a respective supporting surface. The user can act on the set of faces, by modifying existing faces, creating new faces, deleting some faces, and/or defining constraints on faces and/or between faces, or any actions of the like provided by the CAD system at use.
B-Reps may imply a high amount of data. Notably, B-Reps can comprise more and more elements in modern designs, leading to an increasing size of the data structures describing 3D modeled objects modeled by a B-Rep. A B-Rep of great size both takes a lot of memory space and is difficult to transmit. This is particularly an issue in the context of collaborative design. Therefore, compression methods have been developed to decrease the size of B-Reps.
Existing data compression methods of B-Rep models can be sorted into several categories. The first one deals with polygonal meshes, mainly triangles. Many research papers and patent documents are related to this technology. Document EP 0964364 A2 is a typical example. Not only the logical arrangement of triangles is compressed, but also numerical data such as point coordinates, normal vectors, texture codes and other attributes. The second category deals with accurate data, as opposed to approximate data. Accurate data compression deals with NURBS curves and surfaces as basic components of the B-Rep model. Control polygon of NURBS surface is compressed through an incremental definition of points coordinates. The variation of neighboring control points coordinates is “small” and can be coded with fewer digits because of the smoothness of NURBS surfaces involved in industrial applications. A typical example is document EP 2387004 A1. Other solutions comprise data structure preprocessing in order to make existing compression techniques more efficient. Document WO 2011/103031 A1 is an example.
However, at least some of these existing data compression methods may be inoperative in some cases. In any case, the compression ratio may be increased by a new compression technique acting differently from existing techniques.
Thus, the invention aims at improving the compression of 3D modeled objects.